Papermaking process employing carboxylated cellulosic fibers

ABSTRACT

A papermaking process includes, firstly, providing carboxylated cellulosic fibers with a carboxyl group content being in the range from 0.06 to 1.5 mmol/g. Then the carboxylated cellulosic fibers are employed to prepare mixing pulp including filler particles, wherein the content of the carboxylated cellulosic fibers in the mixing pulp is in the range from 40% to 100% by dry fiber weight of the mixing pulp. After that, paper is made employing the mixing pulp.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to People's Republic ofChina Patent Application No. 201310129816.X, Ser. No. 2013041600769200,filed Apr. 15, 2013, which is hereby incorporated by reference herein inits entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to papermaking processes.

2. Description of Related Art

Generally, retention agents including acrylamide and starch are used toimprove the filler particle retention rate of paper pulp. However, forprecipitated calcium carbonate (PCC) and other filler particles havingsmaller particle size, the filler particle retention effect of theretention agents is weaker than for filler particles having largerparticle size, such as ground calcium carbonate and kaolin.

Therefore, what is needed is a papermaking process which can effectivelyimprove the retention rate of precipitated calcium carbonate and otherfiller particles having smaller particle size.

DETAILED DESCRIPTION

In one embodiment, the present disclosure provides a papermaking processwhich includes the following steps:

Step 1: providing carboxylated cellulosic fibers with carboxyl groupcontent being in the range from 0.06 to 1.5 mmol/g (millimoles/gram).

In this embodiment, the carboxylated cellulosic fibers are obtained fromplant fibers modified by a TEMPO (2,2,6,6-tetramethyl-piperidine-1-oxyl)catalytic oxidation system. In the present disclosure, the plant fibersinclude softwood, hardwood, grass fiber, and other plant fiber rawmaterial. In this embodiment, the plant fibers are softwood, hardwood,or a mixture thereof, and the carboxyl group content of the carboxylatedcellulosic fibers is in the range from 0.15 to 0.5 mmol/g.

In this embodiment, the TEMPO catalytic oxidation system comprisescatalyst, oxidant, and assistant catalyst. The catalyst is TEMPO orderivatives of TEMPO. The oxidant is one or more items selected from thegroup consisting of hypochlorite, chlorite, chlorate, hydrogen peroxide,and chlorine dioxide. The assistant catalyst consists of iodides,bromides, or a mixture thereof.

The plant fibers are a polyhydroxy compounds, and each chain of theglucose of the plant fibers has three active hydroxyl groups (—OH)including a primary hydroxyl group and two secondary hydroxyl groups.Generally, the primary hydroxyl groups and secondary hydroxyl groups canall be oxidized to carboxyl groups (—COOH). Different types of hydroxylgroups have different oxidation mechanisms. Thus, according to differentneeds, the oxidation system can be a non-selective oxidation system or aselective oxidation system.

The non-selective oxidation system is a kind of oxidation system whichcan oxidize both the primary hydroxyl groups and the secondary hydroxylgroups to carboxyl groups. The non-selective oxidation system canutilize one or more items from the group consisting of sodiumhypochlorite, hydrogen peroxide, and persulfate. The selective oxidationsystem is a kind of oxidation system which can selectively oxidize thesecondary hydroxyl groups or the primary hydroxyl groups to carboxylgroups. Oxidation systems which can selectively oxidize the primaryhydroxyl groups to carboxyl groups are selected from the groupconsisting of a TEMPO catalyst oxidation system, a hypochloriteoxidation system, an NO₂ and N₂O₄ series of nitric oxide oxidationsystem, and an oxidation system containing sodium bromate, sodiumchlorate and sodium chlorite. Oxidation systems which can selectivelyoxidize the secondary hydroxyl groups to carboxyl groups utilize oneitem or both items selected from the group consisting of periodic acidsand periodate.

Step 2: employing the carboxylated cellulosic fibers to prepare mixingpulp with filler particles added therein, wherein the content ofcarboxylated cellulosic fibers in the mixing pulp is in the range from40% to 100% by dry fiber weight of the mixing pulp.

In this embodiment, the content of carboxylated cellulosic fibers in themixing pulp is in the range from 40% to 50% by dry fiber weight of themixing pulp.

In this embodiment, the content of filler particles in the mixing pulpis in the range from 1% to 80% by dry fiber weight of the mixing pulp.Typically, it is desired that the content of filler particles in themixing pulp is in the range from 20% to 60% by dry fiber weight of themixing pulp. It is to be understood that the content of filler particlesin the mixing pulp can be changed according to practical needs.

Step 3: making paper employing the mixing pulp.

Unlike with conventional processes, in the above-described papermakingprocess of the present disclosure, the carboxylated cellulosic fiberswith carboxyl group content being in the range from 0.06 to 1.5 mmol/gare used as the main fiber of the mixing pulp to make paper, which thecontent of the carboxylated cellulosic fibers in the mixing pulp beingin the range from 40% to 100% by dry fiber weight of the mixing pulp.The much content of the carboxylated cellulosic fibers in the mixingpulp and the large number of carboxyl groups of the carboxylatedcellulosic fibers are able to not only improve the swelling of fibers ofthe mixing pulp and enhance the binding force between fibers so as toform a denser fibrous network structure in the mixing pulp, but alsoenhance the binding force between the fibers and the filler particles.Due to the denser fibrous network structure and the greater bindingforce between the fibers and the filler particles, the mixing pulp canobtain excellent filler retention performance and the final paperproduct can obtain higher filler content.

INTRODUCTION TO EXAMPLES

Three sets of examples are provided. In the following three sets ofexamples, the plant fiber type is LBKP (Laubh{hacek over (o)}lxerbleached kraft pulp), the concentration of paper pulp is 1%, the mixerspeed is 900 rpm (revolutions per minute), the mixing time is 3 mins(minutes), the term “non-oxidative LBKP pulp” means that the LBKP hasnot been modified by an oxidation system, and the term “oxidative LBKPpulp” means that the LBKP has been modified by an oxidation system.

First Set of Examples

The first set of examples is provided to compare ash content and ashretention rate between final paper products made respectively from: (i)non-oxidative LBKP pulp; and (ii) oxidative LBKP pulp having differentcarboxyl amounts; wherein all the examples have the same filler contentand the same LBKP pulp content.

Comparative Example 1

Preparing mixing pulp with non-oxidative LBKP pulp, and with PCC fillerin the amount of 45% by dry fiber weight of the mixing pulp; makingpaper employing the mixing pulp; and testing the ash content and ashretention rate of the final paper product.

Application Example 1

Preparing mixing pulp with oxidative LBKP pulp having a carboxyl groupcontent of 0.2 mmol/g, and with PCC filler in the amount of 45% by dryfiber weight of the mixing pulp, wherein the content of the oxidativeLBKP pulp is the same as the content of the non-oxidative LBKP pulp usedin comparative example 1; making paper employing the mixing pulp; andtesting the ash content and ash retention rate of the final paperproduct.

Application Example 2

Preparing mixing pulp with oxidative LBKP pulp having a carboxyl groupcontent of 0.7 mmol/g, and with PCC filler in the amount of 45% by dryfiber weight of the mixing pulp, wherein the content of the oxidativeLBKP pulp is the same as the content of the non-oxidative LBKP pulp usedin comparative example 1; making paper employing the mixing pulp; andtesting the ash content and ash retention rate of the final paperproduct.

Application Example 3

Preparing mixing pulp with oxidative LBKP pulp having a carboxyl groupcontent of 1.5 mmol/g, and with PCC filler in the amount of 45% by dryfiber weight of the mixing pulp, wherein the content of the oxidativeLBKP pulp is the same as the content of the non-oxidative LBKP pulp usedin comparative example 1; making paper employing the mixing pulp; andtesting the ash content and ash retention rate of the final paperproduct.

Second Set of Examples

The second set of examples is provided to compare ash content and ashretention rate between final paper products made respectively fromnon-oxidative LBKP pulp and oxidative LBKP pulp. Three pairs of examplesare provided. In each pair, the non-oxidative LBKP pulp content and theoxidative LBKP pulp content are the same, and the filler content is thesame. Across the three pairs, three different filler contents areemployed.

Comparative Example 1

Preparing mixing pulp with non-oxidative LBKP pulp, and with PCC fillerin the amount of 5% by dry fiber weight of the mixing pulp; making paperemploying the mixing pulp; and testing the ash content and ash retentionrate of the final paper product.

Application Example 1

Preparing mixing pulp with oxidative LBKP pulp having a carboxyl groupcontent of 0.2 mmol/g, and with PCC filler in the amount of 5% by dryfiber weight of the mixing pulp, wherein the content of the oxidativeLBKP pulp is the same as the content of the non-oxidative LBKP pulp usedin comparative example 1; making paper employing the mixing pulp; andtesting the ash content and ash retention rate of the final paperproduct.

Comparative Example 2

Preparing mixing pulp with non-oxidative LBKP pulp, and with PCC fillerin the amount of 40% by dry fiber weight of the mixing pulp, wherein thecontent of the non-oxidative LBKP pulp is the same as the content of thenon-oxidative LBKP pulp used in comparative example 1; making paperemploying the mixing pulp; and testing the ash content and ash retentionrate of the final paper product.

Application Example 2

Preparing mixing pulp with oxidative LBKP pulp having a carboxyl groupcontent of 0.2 mmol/g, and with PCC filler in the amount of 40% by dryfiber weight of the mixing pulp, wherein the content of the oxidativeLBKP pulp is the same as the content of the non-oxidative LBKP pulp usedin comparative example 2; making paper employing the mixing pulp; andtesting the ash content and ash retention rate of the final paperproduct.

Comparative Example 3

Preparing mixing pulp with non-oxidative LBKP pulp, and with PCC fillerin the amount of 80% by dry fiber weight of the mixing pulp, wherein thecontent of the non-oxidative LBKP pulp is the same as the content of thenon-oxidative LBKP pulp used in comparative example 1; making paperemploying the mixing pulp; and testing the ash content and ash retentionrate of the final paper product.

Application Example 3

Preparing mixing pulp with oxidative LBKP pulp having a carboxyl groupcontent of 0.2 mmol/g, and with PCC filler in the amount of 80% by dryfiber weight of the mixing pulp, wherein the content of the oxidativeLBKP pulp is the same as the content of the non-oxidative LBKP pulp usedin comparative example 3; making paper employing the mixing pulp; andtesting the ash content and ash retention rate of the final paperproduct.

Third Set of Examples

The third set of examples is provided to compare ash content and ashretention rate between final paper products made respectively fromdifferent contents of oxidative LBKP pulp having a carboxyl groupcontent of 0.2 mmol/g, wherein all the examples have the same fillercontent.

Application Example 1

Preparing mixing pulp with non-oxidative LBKP pulp, with oxidative LBKPpulp in the amount of 5% by dry fiber weight of the mixing pulp, andwith PCC filler in the amount of 45% by dry fiber weight of the mixingpulp; making paper employing the mixing pulp; and testing the ashcontent and ash retention rate of the final paper product.

Application Example 2

Preparing mixing pulp with non-oxidative LBKP pulp, with oxidative LBKPpulp in the amount of 40% by dry fiber weight of the mixing pulp, andwith PCC filler in the amount of 45% by dry fiber weight of the mixingpulp; making paper employing the mixing pulp; and testing the ashcontent and ash retention rate of the final paper product.

Application Example 3

Preparing pulp with 100% oxidative LBKP pulp, and with PCC filler in theamount of 45% by dry fiber weight of the oxidative LBKP pulp; makingpaper employing the pulp; and testing the ash content and ash retentionrate of the final paper product.

Results

The test results of the three sets of examples are summarized in thefollowing table.

ash ash content retention rate The first Comparative example 1 8.93%21.79% set of non-oxidative LBKP pulp + examples 45% PCC Applicationexample 1 19.86% 55.07% oxidative LBKP pulp (carboxyl group content is0.2 mmol/g) + 45% PCC Application example 2 22.16% 63.26% oxidative LBKPpulp (carboxyl group content is 0.7 mmol/g) + 45% PCC Applicationexample 3 28.98% 90.68% oxidative LBKP pulp (carboxyl group content is1.5 mmol/g) + 45%PCC The second Comparative example 1 0.82% 16.54% setof non-oxidative LBKP pulp + examples 5% PCC Application example 1 3.64%33.35% oxidative LBKP pulp (carboxyl group content is 0.2 mmol/g) + 5%PCC Comparative example 2 9.28% 25.57% non-oxidative LBKP pulp + 40% PCCApplication example 2 20.28% 55.92% oxidative LBKP pulp (carboxyl groupcontent is 0.2 mmol/g) + 40% PCC Comparative example 3 17.12% 25.82%non-oxidative LBKP pulp + 80% PCC Application example 3 37.09% 67.57%oxidative LBKP pulp (carboxyl group content is 0.2 mmol/g) + 80% PCC Thethird Application example 1 13.26% 33.68% set of mixing pulp including5% examples oxidative LBKP pulp (carboxyl group content is 0.2 mmol/g)and 45% PCC Application example 2 24.08% 67.43% mixing pulp including40% oxidative LBKP pulp (carboxyl group content is 0.2 mmol/g) and 45%PCC Application example 3 24.86% 65.85% pulp being 100% oxidative LBKPpulp (carboxyl group content is 0.2 mmol/g) and 45% PCC

The test results of the first set of examples demonstrate that the ashcontent and ash retention rate of final paper products made from theoxidative LBKP pulp are much higher than the ash content and ashretention rate of final paper products made from the non-oxidative LBKPpulp.

It can be seen from the test results of the second set of examples thaton condition that the content of carboxyl groups of the oxidative LBKPpulp is kept the same and when the filler content used in the paper pulpis varied, the ash content and ash retention rate of final paperproducts made from the oxidative LBKP pulp are much higher than the ashcontent and ash retention rate of final paper products made from thenon-oxidative LBKP pulp, no matter how much filler content is used inthe paper pulp.

It is also seen from the test results of the third set of examples thaton condition that the content of oxidative LBKP pulp having the samecontent of carboxyl groups is progressively increased, the ash contentand ash retention rate of final paper products show an obvious increaseat first and later trend toward stable values.

Combining the above-described test results of the three sets ofexamples, it can be concluded that the papermaking process provided bythe present disclosure greatly improves the retention rate of theprecipitated calcium carbonate and other filler particles which havesmaller particle size, by using the carboxylated cellulosic fibers whosecarboxyl group content is in the range from 0.06 to 1.5 mmol/g as a partof or all of the main fiber to make paper.

It is to be understood that, according to different needs, acrylamide,starch and other retention agents commonly used in the field ofpapermaking can also be used in the papermaking process of the presentdisclosure to further improve the filler retention rate of the paperpulp.

It is to be further understood that even though numerous characteristicsand advantages of the present embodiments have been set forth in theforegoing description, together with details of the structures andfunctions of the embodiments, the disclosure is illustrative only, andchanges may be made in detail, especially in matters of arrangement ofparts within the principles of the disclosure to the full extentindicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. A papermaking process comprising: providingcarboxylated cellulosic fibers with carboxyl group content being in therange from 0.06 to 1.5 millimoles/gram; employing the carboxylatedcellulosic fibers to prepare mixing pulp with filler particles addedtherein, the content of carboxylated cellulosic fibers in the mixingpulp being in the range from 40% to 100% by dry fiber weight of themixing pulp; and making paper employing the mixing pulp.
 2. Thepapermaking process of claim 1, wherein the carboxyl group content ofthe carboxylated cellulosic fibers is in the range from 0.15 to 0.5millimoles/gram.
 3. The papermaking process of claim 1, wherein thecontent of the carboxylated cellulosic fibers in the mixing pulp is inthe range from 40% to 50% by dry fiber weight of the mixing pulp.
 4. Thepapermaking process of claim 1, wherein the content of the fillerparticles in the mixing pulp is in the range from 1% to 80% by dry fiberweight of the mixing pulp.
 5. The papermaking process of claim 1,wherein the content of the filler particles in the mixing pulp is in therange from 20% to 60% by dry fiber weight of the mixing pulp.
 6. Thepapermaking process of claim 1, wherein the carboxylated cellulosicfibers are obtained from plant fibers modified by a non-selectiveoxidation system that oxidizes both primary hydroxyl groups andsecondary hydroxyl groups of the plant fibers to carboxyl groups.
 7. Thepapermaking process of claim 6, wherein the non-selective oxidationsystem utilizes one or more items selected from the group consisting ofsodium hypochlorite, hydrogen peroxide, and persulfate.
 8. Thepapermaking process of claim 1, wherein the carboxylated cellulosicfibers are obtained from plant fiber modified by a selective oxidationsystem that selectively oxidizes primary hydroxyl groups or secondaryhydroxyl groups of the plant fiber to carboxyl groups.
 9. Thepapermaking process of claim 8, wherein in the case that the selectiveoxidation system selectively oxidizes primary hydroxyl groups tocarboxyl groups, the selective oxidation system is selected from thegroup consisting of a TEMPO (2,2,6,6-tetramethyl-piperidine-1-oxyl)catalytic oxidation system, a hypochlorite oxidation system, an NO₂ andN₂O₄ series of nitric oxide oxidation system, and an oxidation systemcontaining sodium bromate, sodium chlorate and sodium chlorite.
 10. Thepapermaking process of claim 8, wherein in the case that the selectiveoxidation system selectively oxidizes secondary hydroxyl groups tocarboxyl groups, the selective oxidation system utilizes one item orboth items selected from the group consisting of periodic acid andperiodate.